LeetCode--No.263--Ugly Number

Write a program to check whether a given number is an ugly number.

Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 6, 8 are ugly while 14 is not ugly since it includes another prime factor 7.

Note that 1 is typically treated as an ugly number.

public class Solution {
    public boolean isUgly(int num) {
        if (num <=0)
            return false;
        while(num % 2 == 0)
            num = num/2;
        while(num % 3 == 0)
            num = num/3;
        while(num % 5 == 0)
            num = num/5;
        return num == 1;
    }
}

这样写会超时。因为会进行很多不必要的判断条件。

public class Solution {
    public boolean isUgly(int num) {
        if (num <=0)
            return false;
        if (num<=5)
            return true;
        while(num >=5){
            if(num % 2 == 0)
                num /= 2;
            if(num % 3 == 0)
                num /= 3;
            if(num % 5 == 0)
                num /= 5;
        }
        if(num < 5)
            return true;
        else
            return false;
    }
}